From the image that expansion looks like it just connected into the trap door expansion under the A600. You could email Amikit to ask them before you order it as they are a great bunch of guys and will answer any questions you might have.

It looks like a useful expansion too as it has a built in clockport for using some A1200 expansions such as USB ports.

For WHDLoad, it contains it's own downgrader built in and will downgrade the system to make older games run on the A600 without you needing to use any floppy disk downgraders.

The IDE to USB connector I mentioned it for accessing a 2.5" harddrive on the PC. You could equally use an external harddrive caddie on the PC to do the same.

The idea is to buy a 2.5" harddrive that will fit inside the A600. Then connect this to the PC using either an external harddrive caddie or an IDE to USB cable. Then using the Amiga emulator WinUAE you can format and setup the harddrive easily on the PC. And then once completed you can remove the harddrive from the PC and put it into the Amiga to enjoy the HD you have then set up.

It sounds more complex than it really is. I can create a guide in the next week or so for you if you need it.